-----Original Message-----
From: byungchul.park [mailto:byungchul.park@lge.com]
Sent: Wednesday, January 18, 2017 9:15 PM
To: 'Peter Zijlstra'
Cc: 'Boqun Feng'; 'mingo@kernel.org'; 'tglx@linutronix.de';
'walken@google.com'; 'kirill@shutemov.name'; 'linux-
kernel@vger.kernel.org'; 'linux-mm@kvack.org'; 'iamjoonsoo.kim@lge.com';
'akpm@linux-foundation.org'; 'npiggin@gmail.com'
Subject: RE: [PATCH v4 15/15] lockdep: Crossrelease feature documentation

quoted

-----Original Message-----
From: Peter Zijlstra [mailto:peterz@infradead.org]
Sent: Wednesday, January 18, 2017 9:08 PM
To: Byungchul Park
Cc: Boqun Feng; mingo@kernel.org; tglx@linutronix.de; walken@google.com;
kirill@shutemov.name; linux-kernel@vger.kernel.org; linux-mm@kvack.org;
iamjoonsoo.kim@lge.com; akpm@linux-foundation.org; npiggin@gmail.com
Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature

documentation

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On Wed, Jan 18, 2017 at 08:54:28PM +0900, Byungchul Park wrote:

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On Wed, Jan 18, 2017 at 12:03:17PM +0100, Peter Zijlstra wrote:

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On Wed, Jan 18, 2017 at 07:53:47PM +0900, Byungchul Park wrote:

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On Wed, Jan 18, 2017 at 02:42:30PM +0800, Boqun Feng wrote:

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On Fri, Dec 09, 2016 at 02:12:11PM +0900, Byungchul Park wrote:
[...]

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+Example 1:
+
+   CONTEXT X		   CONTEXT Y
+   ---------		   ---------
+   mutext_lock A
+			   lock_page B
+   lock_page B
+			   mutext_lock A /* DEADLOCK */

s/mutext_lock/mutex_lock

Thank you.

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+Example 3:
+
+   CONTEXT X		   CONTEXT Y
+   ---------		   ---------
+			   mutex_lock A
+   mutex_lock A
+   mutex_unlock A
+			   wait_for_complete B /* DEADLOCK */

I think this part better be:

   CONTEXT X		   CONTEXT Y
   ---------		   ---------
   			   mutex_lock A
   mutex_lock A
   			   wait_for_complete B /* DEADLOCK */
   mutex_unlock A

, right? Because Y triggers DEADLOCK before X could run

mutex_unlock().

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There's no different between two examples.

There is..

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No matter which one is chosen, mutex_lock A in CONTEXT X cannot be

passed.

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But your version shows it does mutex_unlock() before CONTEXT Y does
wait_for_completion().

The thing about these diagrams is that both columns are assumed to

have

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the same timeline.

X cannot acquire mutex A because Y already acquired it.

In order words, all statements below mutex_lock A in X cannot run.

But your timeline shows it does, which is the error that Boqun pointed
out.

I am sorry for not understanding what you are talking about.

Do you mean that I should remove all statements below mutex_lock A in X?

Or should I move mutex_unlock as Boqun said? What will change?

Anyway, I will change it as he said even though I don't understand what is
different between them. :/ But I am just curious. It would be appreciated
if you answer my question.


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